1. Field of the Invention
This invention relates to a method for the wet slaking of calcium and magnesium oxides from calco-magnesian compounds preferably containing at least 10% by weight of MgO relative to the total weight of said calco-magnesian compound, comprising the steps of:                feeding said calco-magnesian compound containing MgO into a slaking equipment;        feeding an aqueous slaking phase into said slaking equipment; and        slaking the said calcium and magnesium oxides of the said calco-magnesian compound fed into the said slaking equipment, with said aqueous slaking phase, leading to the formation of slaked solid particles of calcium and magnesium hydroxides (e.g. of general formula xCa(OH)2.yMg(OH)2).        
2. Description of the Prior Art
Typically, the slaking of MgO to form Mg(OH)2, compared with conventional slaking of CaO to form Ca(OH)2, is a difficult reaction to carry out profitably at industrial level. One of the possible routes to produce fully hydrated products, namely in which MgO and CaO are fully converted to Mg(OH)2 and Ca(OH)2 respectively, is high pressure hydration, during which a supply of heat is sometimes necessary as a function of the reactivity of the MgO. In some cases during slaking in a wet process, very lengthy reaction times may overcome these drawbacks. However, the use of high pressure hydrators with or without the supply of heat, or lengthy residence times are as many obstacles which reduce the industrial production of magnesium hydroxide from MgO, the preference being given to the chemical production of Mg(OH)2 from salts treated with caustic solutions.
Just as there exist limestone deposits (calcium carbonate of formula CaCO3), there also exist dolomite deposits (mixed calcium and magnesium carbonate of general formula xCaCO3.yMgCO3 where x and y are molar coefficients such that x/y=0.8 to 1.2), and deposits of other mixed carbonates of general formula xCaCO3.yMgCO3 where 1.2≦x/y≦25) or any other mixed carbonate of calcium and magnesium. In the same manner as for limestone, dolomite or the other aforementioned mixed carbonates can be calcined, thereby producing dolomitic quicklime of formula xCaO.yMgO or any other mixed calcium and magnesium oxide. Similar to quicklime, a hydration reaction is initiated when dolomitic quicklime or other aforementioned mixed oxide is contacted with water. However, as mentioned above, it is known that magnesium oxide has much lower reactivity to water than high calcium quicklime that is highly hydrophilic, the hydration of these calcined compounds thereby becoming much more complex than the hydration of high calcium quicklime.
As mentioned above, to obtain a fully hydrated product by a wet process, persons skilled in the art currently have recourse to a hydrothermal hydration process using an aqueous phase pre-heated to a temperature typically of between 40 and 80° C. for an extended reaction time (typically 5 to 48 h). Another possible process, to which skilled persons may have recourse, is a high pressure hydration process. At industrial level the first option is preferred, although the residence time and the quality of the hydrated product are highly dependent on the reactivity of the oxides in the initial compound.
In all cases, these slaking processes are complex and costly and are detrimental to the industrial treatment of these MgO-containing compounds to obtain compounds containing Mg(OH)2, with the risk that a portion of the MgO will not be properly hydrated.
FR2669327 A1 teaches the use of chemical agents such as amines or glycols to produce a hydrated lime at regulated or controlled temperature having improved plastic properties and high specific surface areas.
WO09209528 also concerns the use of additives selected from among glycols and/or amines to produce calcium and/or magnesium hydroxides having high specific surface areas.
U.S. Pat. No. 3,120,444 discloses the addition of low molecular weight aliphatic alcohols to obtain hydrated lime with improved plastic properties.
U.S. Pat. No. 1,856,763 discloses a method to produce quicklime of high purity with delayed reactivity for use thereof in mortars.
It is the objective of the invention to overcome the shortcomings of the prior art by providing a method allowing the simple, low-cost production of a compound via wet process that can be implemented at industrial level, the compound containing slaked solid particles of Mg(OH)2 whereby hydration is accelerated and/or whereby the rate of conversion of MgO oxide to the hydroxide Mg(OH)2 is increased.